P0777 Pressure Control Solenoid B Stuck On
OBD-II Trouble Code Technical Description
Former Service Manager & Air Force Mechanic
Pressure Control Solenoid B Stuck On
What does that mean?
This is a generic transmission diagnostic trouble code (DTC) and typically applies to OBD-II vehicles equipped with an automatic transmission.
That may include but is not limited to vehicles from Ford, Mercury, Lincoln, Jaguar, Chevrolet, Toyota, Nissan, Allison/Duramax, Dodge, Jeep, Honda, Acura, etc. Although generic, the exact repair steps may vary depending on year, make, model and powertrain configuration.
When the P0777 OBD-II trouble code is set, the Powertrain Control Module (PCM) has detected a problem with the Transmission Pressure Control Solenoid "B". Most automatic transmissions incorporate at least three solenoids that are solenoid A, B and C. The trouble codes related to the "B" solenoid are codes P0775, P0776, P0777, P0778 and P0779. The code set is based on the specific malfunction that alerts the PCM and illuminates the Check Engine Light.
The purpose of the Transmission Pressure Control Solenoids is to control the pressure of the fluid for the proper operation of an automatic transmission. The PCM receives an electronic signal based on the pressure within the solenoids. An automatic transmission is controlled by bands and clutches that change gears by having fluid pressure in the right place at the right time. Based on the signals from associated devices monitoring the speed of the vehicle, the PCM controls the pressure solenoids to direct fluid at the appropriate pressure to various hydraulic circuits that change the transmission gear ratio at the correct time.
The code P0777 is set by the PCM when the Pressure Control Solenoid "B" is stuck in the "On" position.
Example of a transmission pressure control solenoid:
What is the severity of this DTC?
The severity of this code normally starts as moderate, but it can progress to a more severe level rapidly when not corrected in a timely manner.
What are some of the symptoms of the code?
Symptoms of a P0777 trouble code may include:
- Vehicle enters limp mode
- Transmission slips when shifting
- Transmission overheating
- Transmission catches in gear
- Decreased fuel economy
- Possibly misfire-like symptoms
- Check Engine Light illuminated
What are some of the common causes of the code?
Causes for this P0777 transmission code may include:
- Defective Pressure Control Solenoid
- Dirty or contaminated fluid
- Dirty or clogged transmission filter
- Defective Transmission Pump
- Defective Transmission Valve Body
- Restricted hydraulic passages
- Corroded or damaged connector
- Faulty or damaged wiring
- Faulty PCM
What are some P0777 troubleshooting steps?
Prior to beginning the troubleshooting process for any malfunction you should research the Technical Service Bulletins (TSB's) for the specific vehicle by year, model and transmission. In some circumstances this can save a lot of time in the long run by pointing you in the right direction. You should also check the vehicle records to verify the last time that the filter and fluid was changed if possible.
Fluid & Wiring Inspections
The first step is to check the fluid level and examine the condition of the fluid for contamination. Prior to changing the fluid, you should check the vehicle records to verify the last time that the filter and fluid was changed.
A detailed visual inspection to check the condition of the wiring for obvious defects is next. Check the connectors and connections for security, corrosion and damaged pins. This should include all wiring and connectors to the transmission pressure control solenoids, the transmission pump and the PCM. Depending on the configuration, the transmission pump may be electrically driven or mechanical driven.
The advanced steps always become very vehicle specific and require the appropriate advanced equipment to perform accurately. These procedures require a digital multi meter and the specific technical references for the vehicle. You should obtain the specific troubleshooting guidelines for your vehicle prior to proceeding with the advanced steps. Voltage requirements may very based on the specific model of the vehicle. Fluid pressure requirements will also vary based on the transmission design and configuration.
Unless otherwise specified by the technical data, the normal readings for wiring and connections should be 0 ohms of resistance. Continuity checks should always be performed with the power removed from the circuit to avoid shorting the circuit and creating more damage. Resistance or no continuity is an indication of faulty wiring that is open or shorted and must be repaired or replaced.
What are some common repairs for this code?
- Changing the fluid and filter
- Replace faulty Pressure Control Solenoid
- Repair or replace a faulty transmission pump
- Repair or replace defective transmission valve body
- Transmission flush to clean passages
- Cleaning corrosion from connectors
- Repairing or replacing wiring
- Flashing or replacing PCM
Possible misdiagnosis may include:
- Engine misfire problem
- Transmission pump problem
- Internal transmission problem
- Driveline problem
Hopefully, the information in this article has been helpful to point you in the right direction to correct the problem with your pressure control solenoid trouble code. This article is strictly informational and the specific technical data and service bulletins for your vehicle should always take priority.
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